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30 watt +20 db lineair met mrf 237 & mrf 238 fm/cw.

click for enlarging concerning this design:

 Taken over at these a design from: Motorola engineering Bulletin.

This schematics build already several times by several amateurs with good result have been built. , however, this end staircase does not pay attention for S.S.B or A.M. to that use suitable is there the transistors in class C stand! The schematics can be built on dubbelsided print of 6 X, held with purchaser, 10 mm. The wheel staircase works with VHF capacity transistor type of MRF 237 in TO-39 a housing, the emitter have been put through with the housing, (these are soldered in the print to the back of the print and have no further refrigeration necessary.) all self-inductions with exception of the suffocating reels and L5 have been carried out as stripline (therefore component of the pressed wiring). Under the pressed reels the purchaser layer has been removed to lose to limit.

The amplifier: THE MRF 238 are 30 Watt capacity transistor for V.H.F. that 10 Db have strengthening.  Very important in this type designs is sufficient mass suggesting area of the print surface.  At the most important places the copper must be solderd above and lower part is put together (domít use  too thin wire.)

The condensators which C7 forms must be assembled as closely as possible to the basis connection of the MRF 238.  Also they must be loss arm, for example ceramic chip condensers.  Important also a good quality trimmers has been arranged for example ARCO or use airtrimmers for this capacity and these band.  THE MRF 238 must be assembled on coolingplate.  To the termination tunnebale a PI filter has been chosen for oppressing harmonics.  Advisable to place that between the end staircase still an extra filter the oppression of the harmonischen now on such a -35 Db lies improve still further.

Much attention in this design has been given on oppressing the notorious spurious oscillations:  Among other things by good HF separation of both transistors, disconnecting the feeding lines and the way the have been dimensioned.

Componenten30 Watt Lineair.

Q1 MRF 237 RFC 2 10 turns. No. 20 AWG ,Enameled on 470-ohm ,1/2 W Resistor with Ferrite Bead Ferroxcube 5659065/48
Q2 MRF 238
C1 0.001 uF 50 V Erie Disc RFC 3 10 turns No 20 AWG, enameled on 270 -ohm 1/2 W resistor with Ferrite Bead Ferroxcube 5659065/48
C2 39 pF Dipped MICA RFC 5 Ferroxcube VK20020/4B
C3 24 pF Dipped MICA L1 (3.30 X 0.254 cm)Airline inductor
C4 91 pF Dipped MICA L2 (1.52 X 0.254 cm ) Airline inductor
C5 8 - 60 pF ARCO 404 Trimmer L3 Base Lead Q1
C6,C10 15-115 pF ARCO 406 Trimmer
C7 250 pF and 100 pF UNELCO in Parallel L4 Collector Lead Q1
C8,12,14 0.1 uF ,50-Vdc ,Erie Disc
C9 82 pF Dipped MICA L5 Airline Inductor and 1-turn No .18 AWG   (0,64 cm) I.D.
C11 500 pF Dipped MICA L6 (4,83 X 0,254 cm ) Airline inductor
C13 0,018 uF Chip L7 (1,78 X 0,254 cm ) Airline inductor
C15 1 uF 35 Vdc Tantalum L8 (2,29 X 0,254 cm ) Airline Inductor
C16 680 pF Allen-Bradley Feedthrough L9 (3,56 X 0,254 cm) Airline Inductor
C17 100 pF Dipped MICA L10 10 turns ,No 20 AWG ,Enameled Wire (0.59 cm) I.D.
R1 150 Ohm 1/2 Watt (koolweerstand !)
RFC 1,4 0,15 uH Molded Choke with Ferrite Bead  Ferroxcube 5659065/4B
P.S. De component waarden en typen zijn onvertaald gelaten ...

Print Layout lineair:

tunning of this amplifier:

Above the dubbelsided epoxy prints lay-out (6 * 10 cm dimensions).
If the complete switching is built is possible these becomes tunned, dummyload and capacities/SWR meter are for this necessary.
It closes linearly just on a antenna if you are certain that and an other one works well and stably.

Feeding must be stabillised and ongoing 5 amps are possible provide at 13.8 volt.
The trimmers must be put on maximum capacity. (with trimkeys of plastic therefore no metal propeller turner!)
There such a quarter a up to half Watt must be sent in. (More capacity can blow up the entrance transistor.)
At 300 mW the maximum capacity of 30 Watt is already reached.


Posted by beheerder on 07. August 2009 21:24 Posted by beheerder on 07. August 2009 21:24 13331 Reads Print
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